MOUNTING OBJECTS IN CANADA BALSAM. 231 



or camel-hair brush. Such a transfer will often be found advan- 

 tageous, before the final completiou of the reducing process ; for 

 it will occasionally happen that we find something in the struc- 

 ture of the specimen, which will be best displayed by rubbing it 

 down afresh on the side first attached to the glass ; and, when a 

 number of small sections are being made at once (which it is 

 often very convenient to do, not only in the case already men- 

 tioned, § 108, but in many others), it not only saves time, but 

 insures the accurate flattening of the surface in grinding, to fix 

 several -upon the same slip, and to work them down together, 

 until the requisite thinness has been nearly attained, when they 

 nrast be transferred to separate slips, and finished one by one. 

 In either case, the reattachment must of course be made like 

 the original attachment, with balsam which has been first har- 

 dened (§ 109). 



130. When the Balsam employed in mounting has remained 

 in the liquid condition here recommended, the glass cover will 

 not be secure from displacement until the balsam has become 

 harder. This change it will require a long time to undergo, 

 unless the aid of a gentle continuous warmth be afforded. 

 Nothing is more suitable for this purpose, than the warmth of 

 a chimney-piece immediately above the fire-place ; as it is quite 

 sufficient to produce the effect in the course of a few daj^s, whilst 

 there is no danger of its becoming excessive ; but in default of 

 this convenience, an oven carefully regulated, or (still better) a 

 water-bath, may be employed. Whether either of these means 

 be adopted, or the slides be put aside for the balsam to be 

 hardened by time, they should always be laid in the horizontal 

 position, that their covers may not be caused by gravitation to 

 slip down from their places. It may be better, before submitting 

 the slides to this hardening process, to scrape from their surface 

 any superfluous balsam that does not immediately surround the 

 glass cover ; but the knife should never be carried so near to the 

 edge of this, as to run any risk of displacing it ; and it is much 

 better to defer the final cleaning of the slide, until the attach- 

 ment of the cover has become firm. The remaining balsam may 

 then be scraped away with a knife or small chisel, the imple- 

 ment being warmed if the balsaixi be very stiff; the slide should 

 then be rubbed with a rag dipped in oil of turj)entine, until 

 every perceptible soil of balsam is removed, especial care being 

 taken to cleanse the surface and edges of the glass cover; and as 

 this will itself leave a certain resinous film, it is better to give 

 the slide a final cleansing with Alcohol. If its surface should 

 have been considerably smeared with balsam, it is very con- 

 venient, after scraping away all that can be removed in that 

 manner, to scrub it with a tooth-brush or nail-brush, first letting 

 fall on it a few drops of turpentine or spirit of wine ; and there 

 is less risk of displacing the glass cover in this mode, than in 

 rubbing it in any other way. The menstrua which serve thus to 



